“Aortic aneurysm” is the term used to describe a vascular abnormality condition wherein a segment of the aorta is dilated to a diameter greater than its original diameter. Aneurysms can occur in virtually any region of the vasculature including the aorta in the abdominal and thoracic regions. Aortic aneurysms are caused by hardening of the arteries (atherosclerosis), high blood pressure (hypertension), genetic disposition such as Marfan's Syndrome, trauma or less common disorders. Atherosclerosis is the most common cause.
Where dilation of the aorta meets or exceeds 50% of the original aortic diameter, i.e., where the diameter of the aorta is 150% of the original or expected diameter, intervention generally is deemed necessary. Without intervention, the aneurysm may continue to expand, leading to the possibility of tearing or rupture of the aorta and death. Intervention includes techniques such as replacement of the aorta with a synthetic lumen which is sewn to the two ends of the still viable aorta after the aneurysmal portion has been opened or surgically removed, or, less invasively, by the endovascular placement of an exclusion device such as a stent graft across the aneurysmal site. The stent graft is a tubular member designed to provide a conduit within the aorta enabling blood flow through the aorta without allowing the systemic pressure of the blood to further stretch the aneurysm. For this intervention to be successful, the stent graft must span the weakened blood vessel wall so that the stent grafts' opposed ends engage and seal against healthy blood vessel tissue on the proximal and distal sides of the aneurysm.
A stent graft includes a stent (framework) portion which provides physical support of the stent graft in a tubular configuration once deployed at a vascular location, and a graft portion, comprising an excluding material, which is sewn or otherwise attached to the stent portion and which provides a relatively fluid-tight conduit for blood flow through the stent graft and past the aneurysm site. Placement of a stent graft can be performed without a chest incision, by using specialized catheters that are introduced through arteries usually at a location in a leg adjacent to the groin.
The aorta has numerous arterial branches. For example, the descending aorta includes the superior mesentery artery, the celiac trunk and the renal arteries. The proximity of an aneurysm to a branch artery may limit the use of an excluding device such as a tubular stent graft, as the main body or ends of the tubular stent graft may occlude or block the branch arteries due to the need for positioning of the stent graft at the location of healthy artery wall. Alternatively, there may be an inadequate length of healthy tissue for the stent graft to seal against in the area between the aneurysmal region of the artery and the location of the branch arteries. In this case, even if the stent graft initially is located without blocking a branch artery, there still is a risk of migration of the exclusion device to a position where it may partially or fully block a branch artery. Additionally, where multiple branch arteries are present adjacent to the aneurysm, the ability to position a stent graft so as not to occlude any of the branch arteries may be problematic. Furthermore, the aneurysm may implicate the aortic wall tissue adjacent to the branch arteries, for example the renal arteries, such that the aorta is dilated at the renal arteries, and the stent graft must extend over the renal arteries to have its ends seal against healthy aorta wall tissue.
To enable sealing off of the aneurysm from blood flow and simultaneously prevent occlusion of blood flow to the branch arteries, an artificial branch lumen may extend from the stent graft and into the branch vessel to a position wherein the distal end of the artificial branch lumen may contact and seal against healthy blood vessel tissue in the branch vessel. Thus, where an aneurysm extends adjacent to, or actually implicates, the branch vessel, a stent graft may still be deployed to exclude the aneurysm from further blood flow, by providing the artificial branch lumen to carry the blood flow into the branch lumen. However, the addition of an artificial branch lumen to the stent graft, and the deployment thereof, present additional complications for the physician attempting to successfully exclude the aneurysm. Where the artificial branch lumen is integrally provided with the stent graft, i.e., is affixed or attached to the stent graft main body at the time of deployment of the stent graft, the volume of the artificial branch lumen increases the cross section of the stent graft, thereby necessitating the use of a catheter of a larger crossing profile for deployment of the stent graft. In patient having restricted or diseased arterial anatomy, this increase in the diameter or crossing profile of the delivery catheter may preclude the ability to deploy the stent graft intravascularly, thus preventing treatment with a stent graft.
Alternatively, it may also be possible to first deploy a stent graft to span the aneurysmal location, and include in the stent graft one or more apertures which are then aligned, during deployment, with branch vessel locations which are spanned by the stent graft. Artificial branch lumens may then be located in these apertures, and extend therefrom and into the adjacent branch vessel to provide an artificial flow lumen for blood to flow from within the main body of the stent graft directly into the branch vessel. However, current schemes for providing a seal at the stent graft-artificial branch lumen interface can result unacceptable levels of leakage at the main body branch vessel interface, such that blood at systemic pressure can reach the aneurysm.
One circumstance which contributes to the occurrence of leakage is the situation where the branch vessel does not intersect with the aorta in a right angle or perpendicular relationship. As a result, the artificial branch lumen will need to extend at an acute angle from the sidewall of the stent graft, with a result that it may be difficult or impossible to effect a seal between the artificial branch lumen and the stent graft at the location where the artificial branch lumen extends from the aperture in the stent graft. An additional circumstance occurs where the artificial branch lumen is not properly extended from the stent graft when it is expanded into sealing engagement with the healthy wall tissue of the branch vessel, with the result that the artificial branch lumen may be located inside the lumen and away from the wall of the stent graft at the aperture in the stent graft and thereby fail to seal at the sealing interface of the artificial branch lumen with the stent graft. A sealing element attached to the artificial branch lumen is prevented from close engagement with the interior of the main body at the aperture.